1. Field of the Invention
The present invention relates to a dual-shaft pivot device, and more particularly to a dual-shaft pivot device which can generate guide resilience when two pivotal shafts are turned synchronously in opposite directions to a predetermined angle, such that the two pivotal shafts can be synchronously positioned at the predetermined open angle.
2. Description of the Prior Art
As development and change of various electronic products, a conventional pivot structure with two ends of a single pivotal shaft to connect with a pivot member (screen) and a corresponding pivot member (host) cannot meet the demand of different uses. Thus, a dual-shaft pivot device as shown in FIG. 1 and FIG. 2 is widely used. The dual-shaft pivot device comprises first and second pivotal shafts 30, 40, a fastening assembly 6, a pivot positioning assembly 7, and a pivot limit plate 7. The first and second pivotal shafts 30, 40 each have at least one positioning flat surface 301, 401 which extends from a middle section thereof and a fixing portion 303, 403 (which may be outer threads) at the end. The other ends of the first and second pivotal shafts 30, 40 have a connecting portion 302 connected with a pivot member (screen) and a connecting portion 402 connected with a corresponding pivot member (host).
The fastening assembly 6 comprises a seat 65 and a separate positioning plate 64. The seat 65 and the positioning plate 64 respectively have through holes 651, 652 and through holes 641, 642 for insertion of the first and second pivotal shafts 30, 40. The positioning plate 64 has a slot 643 disposed between the two through holes 641, 642. One side of the seat 65, far away from the positioning plate 64, has resilient portions 61, 62 corresponding in position to the through holes 651, 652. The resilient portions 61, 62 are fitted on the ends having the positioning flat surfaces 301, 401 of the first and second pivotal shafts 30, 40. Fixing members 304, 404 which may be nuts are respectively coupled to the fixing portions (outer threads) 303, 403, such that the first and second pivotal shafts 30, 40 and the seat 65 keep fastening resilience. The seat 65 has a positioning portion 63 (which may be a threaded hole) between the resilient portions 61, 62.
The pivot limit plate 8 is disposed at one side of the seat 65, far away from the two resilient portions 61, 62. The pivot limit plate 8 has through holes 81, 82 corresponding to the through holes 651, 652, stop portions 811, 821 which are respectively disposed on the outer edge of one side of the respective through holes 81, 82 in different directions and angles, and a slot 83 between the two through holes 81, 82.
The pivot positioning assembly 7 is disposed between the pivot limit plate 8 and the positioning plate 64. The pivot positioning assembly 7 comprises two link rollers 71, 72 and a movable roller 73. The two link rollers 71, 72 have central coupling holes 711, 721 to fit on the positioning flat surface 301, 401. The outer wall and one side of the two link rollers 71, 72 have positioning recesses 712, 722 and side protrusions 713, 723, respectively. The two side protrusions 713, 723 are subject to the stop portions 811, 821 to form the pivot limit for different directions and angles. The movable roller 73 has a central protruding axle 731. Two ends of the axle 731 are respectively inserted in the slot 643 and the slot 83 so that the movable roller 73 is movable within the limit area. A resilient plate 74 is provided between the movable roller 73 and the pivot limit plate 8. The resilient plate 74 has a central hole 741 for insertion of the axle 731. By the resilient plate 74, the movable roller 73 and the two link rollers 71, 72 are kept in a tightening contact state.
As shown in FIG. 3 to FIG. 7, when the pivot member (screen) and the corresponding pivot member (host) are closed with each other, the first and second pivotal shafts 30, 40 respectively move the two link rollers 71, 72 with the positioning recesses 712, 722 to face the same side (as shown in FIG. 3). As shown in the drawings, one side of the link roller 71, far away from the positioning recess 712, pushes the movable roller 73 to engage with the positioning recess 722 of the link roller 72. At this time, because the relative arc surfaces of the link roller 71 and movable roller 73 are contact with each other, the first pivotal shaft 30 can be pivoted continuously. During pivotal turning, the second pivotal shaft 40 is unable to pivot (as shown in FIG. 4.) until the first pivotal shaft 30 brings the link roller 71 to a predetermined angle (as shown in drawings, the predetermined angle is 180 degrees). The positioning recess 712 of the link roller 71 is turned to face the movable roller 73 (as shown in FIG. 5) to release the contact with the movable roller 73. This moment, the movable roller 73 can slide along the slots 643, 83 and the second pivotal shaft 40 (the link roller 72) is able to pivot.
After that, the second pivotal shaft 40 brings the link roller 72 to pivot reversely toward the first pivotal shaft 30 (the link roller 71), as shown in FIG. 6. During pivotal turning of the second pivotal shaft 40, the circumferential edge of the link roller 72 is contact with the movable roller 73 for the movable roller 73 to engage with the positioning recess 712 of the link roller 71, such that the first pivotal shaft 30 is unable to pivot until the second pivotal shaft 40 brings the link roller 72 to a predetermined angle (as shown in drawings, the predetermined angle is 180 degrees). The positioning recess 722 of the link roller 72 is turned to face the movable roller 73 (as shown in FIG. 7) to release the contact with the movable roller 73. After use, one of the first and second pivotal shafts 30, 40 can be first pivoted reversely to the original closed state.
However, the aforesaid structure has the following shortcomings:
1. During operating, only the first pivotal shaft 30 (the link roller 71) or the second pivotal shaft 40 (the link roller 72) can be pivoted. When the link roller 71 (or the link roller 72) is not turned to the predetermined angle, the other link roller 72 (or the link roller 71) is unable to turn. This is not convenient for use.
2. When in use, the two link rollers 71, 72 don't have a positioning effect except in a closed state or at a specific angle.
3. During movement, the movable roller 73 cannot be kept stably and may deflect easily to result in noises caused by friction of the two link rollers 71, 72 and the movable roller 73, and the turning is not smooth.
Accordingly, the inventor of the present invention has devoted himself based on his many years of practical experiences to solve these problems.